Note: Descriptions are shown in the official language in which they were submitted.
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A TENSIONING APPARATUS
The present invention relates to a tensioning apparatus and particularly to
an apparatus and a kit for tensioning studs and bolts in bolted joints.
.5
It is commonly known that if bolted joints are not correctly tensioned or
secured together with the correct compressive -force or load, then those
joints are likely to eventually fail or otherwise experience some form of
mechanical fatigue. Accordingly, there are therefore numerous mechanical
problems that may potentially result if a bolted joint is not correctly
tensioned.
Many bolted joints are fastened together by way of a stud, bolt, threaded
rod or shaft having two conventional nuts at either end, which are then
tightened together to attain a desired preload tension in the joint. However,
one of the major problems associated with traditional stud tightening
techniques is as the diameter of the stud increases, the amount of torque
required to tighten it increases exponentially as the third power of the
diameter. Consequently, the largest size stud or bolt that may typically be
tightened by hand is around 3 cm.
To address this problem, the prior art provides several ways of tensioning
studs or bolts without requiring excessive amounts of torque to tighten the
stud or bolt. One popular device is what is known as a 'multi-jackbolt
tensionee, which is a direct replacement for conventional nuts. The device
can be simply threaded onto a new or existing stud, bolt, rod or shaft and
works by using multiple jackbolts or cap screws that are threaded through
the body of the nut or bolt head. Tensioning of the bolted joint is
accomplished by applying torque to each of the jackbolts, which are small
enough to be tightened by simple hand tools. The jackbolts press against a
hardened washer, which transfers the preload evenly into the stud or bolt,
and consequently, onto the bolted joint.
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In this way, collective loads of up to around 100 MN and greater may be
achieved by using only hand tools, such as a torque wrench or a pneumatic
tool. Therefore, it is evident that the use of multi-jackbolt tensioners
provides many benefits over other tightening techniques, not least in that
the bolted joint is tightened in pure tension (i.e. no torsional strain), with
only simple tools being required for tightening; while they can also be
installed in confined spaces (as they are a direct replacement for a nut)
without significant downtime.
However, although multi-jackbolt ten.sioners are reliable and safe devices
for compressing a bolted joint to a desired load, they do have the drawback
that they are costly components (due to having multiple parts and requiring
accurate machining during fabrication) with one tensioner being
permanently required for each stud or bolt to be tensioned. Therefore, if a
mechanical structure comprises a large number of bolted joints, the cost to
tighten each of these may be prohibitive as a tensioner cannot be reused for
subsequent studs or bolts without removing it from the bolted joint.
Hence, it is an object of the present invention to address some, if not all,
of
the above problems in the art, by providing a reusable tensioning apparatus
and kit for tensioning multiple bolted joints without the need to have a
permanent tensioner for each joint.
According to a first aspect of the present invention there is a provided an.
apparatus for tensioning a stud in a bolted joint to a desired preload, the
apparatus comprising:
a locking means adapted for engagement with the stud;
a removable bridge member arranged to at least partially enclose the
locking means and to receive the stud therethrough;
a removable actuator operable to actuate the locking means through
the bridge member; and
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removable tensioning means configured to apply tension to a load
bearing surface of the bridge member so as to transfer tension to the stud;
wherein the actuator is operable to lock the locking means when the
desired preload in the stud is achieved.
The provision of a tensioning apparatus comprising at least some
components that are removable after a desired preload for a stud is
achieved is found to be particularly advantageous, as only a single
tensioner (e.g. multi-jackbolt tensioner etc.) is required to tension multiple
1.0 studs. :By contrast, conventional techniques require a permanent
tensioner
for each and every stud, which must remain in place even after the stud is
tensioned to the desired preload.
Therefore, the present invention allows reuse of the same tensioner, which
avoids the costs of having to acquire multiple tensioners.
It is to be appreciated that the use of the term "stud" herein is intended to
cover all kinds of studs, bolts, threaded rods and shafts, and indeed the
apparatus of the present invention may be used with all kinds of fastening
devices that are typically used to compress bolted joints to a required
tension and where a tensioner of a multi-jackbolt type, for instance, is
conventionally used to apply tension to the joint.
By "bolted joint" we mean any mechanical joint, coupling or connection
between two or more components or mechanical assemblies that may be
fastened or compressed together without lirnitation.
In particularly preferred embodiments, the locking means may be a
threaded nut. The nut is preferably threaded so as to reciprocally engage
the threading of the stud. In this way, the locking means may then be
simply screwed onto the stud.
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The nut may have a circular or hexagonal cross-section. However, any
suitable cross-section may be used.
Preferably, in exemplary embodiments, the nut has a circular cross-section
and comprises at least one radial bore hole through the body of the nut, and
most preferably, comprises a plurality of radial bore holes. By "radial bore
hole" we mean a preferably circular channel through the body of the nut,
such that the channel has an axis that is approximately orthogonal to the
longitudinal axis of the nut. The bore hole may extend fully through the
body of the nut (i.e. open at both ends) or else extend only partially through
the body (i.e. closed at one end -- the end closest to the interior surface of
the nut).
The function of the bore holes is to receive the removable actuator, in that
the actuator may be releasably engaged with the bore hole to enable the nut
to be turned (i.e. scre-w-cd) on the stud so that the nut can be tightened. In
this way, the locking means may be locked when a desired preload is
achieved in the stud, as will be discussed in more detail below.
In preferred embodiments, the removable bridge member is substantially
cylindrical (e.g. tubular) in form and preferably comprises an open end and
a closed end. The circumferential 'lip' of the open end preferably acts as a
'surface' for engaging the planar surface of the bolted joint to be tensioned;
while the closed end preferably includes an open bore (e.g. circular
aperture) for receiving the stud. In other words, the bridge member may be
placed over the stud so that the stud passes through and along the
longitudinal axis of the bridge member.
When the bridge member is placed over the stud, it then at least partially
encloses (or covers) the locking means. In preferred embodiments, the
bridge member comprises at least one aperture or window through which
the actuator may pass to releasably engage with the locking means. The
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aperture is preferably located in a side wall of the bridge member and will
typically take the form of a cut-out or cut-away portion of the bridge
member. Indeed, in particularly preferred embodiments, the aperture may
be a substantially 'U-shaped' cut-out having an 'open edge' that extends to
5 the circumferential lip of the open end of the bridge member.
However, it is to be appreciated that any shape or form of aperture may be
used, provided it allows the actuator access to the locking means.
Moreover, two or more apertures may be used to enable greater access to
the locking means depending on the particular application and
implementation of the present apparatus.
In particularly preferred embodiments, the removable actuator comprises an
elongate rod adapted to engage with at least one of the radial bore holes.
The elongate rod is preferably fabricated from hardened steel and is most
preferably a conventional "tommy bar". The actuator may therefore bc
inserted through the aperture of the bridge member to engage with a bore
hole, enabling the locking means (e.g. nut) to be turned. The actuator may
then be removed and (re-)inserted into the next bore hole which has been
rotated into the aperture. In this way, the nut may be turned and tightened
by repeated application of the tommy bar to the nut.
The use of a tommy bar and circular nut is especially advantageous, as it
allows the nut and bridge member to be respectively sized so that only a
small internal (circumferential) gap exists between them. As a result, the
'foot print' (i.e. diameter) of the bridge member can be kept relatively
small, which allows the present apparatus to be used in confined spaces or
difficult to install locations. By contrast, if the nut were a conventional
hexagonal nut, with the actuator being a wrench or spanner, the spacing
between the nut and the bridge member would need to be considerably
larger to enable the wrench to engage with the nut through the aperture.
Although such an arrangement is not excluded by the present invention,
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this is not preferred. But it is .possible that such an arrangement could be
used in some applications and/or implementations.
The removable tensioning means preferably comprises a jacking nut or a
multi-jackbolt tensioner consisting of a plurality of jackbolts or cap screws.
Indeed, in exemplary embodiments, the tensioner is ideally a nut-type
inulti-jackbolt tensioner having a pitch circle diameter of cap screws as
known in the prior art.
The use of a multi-jackbolt tensioner is beneficial as it allows the many
advantages of this type of tensioner to be utilised in the present
application.
Therefore, the stud may be tensioned to relatively large preload tensions by
the application of only a relatively low torque to each of the cap screws. As
a result, only simple hand tools or pneumatic devices need be used to load
the bolted joint to the required tension. Moreover, as multi-jackbolt
tensioners tighten the stud in pure tension there is no torsional strain.
The apparatus may further comprise a washer removably disposed between
the tensioning means and the bridge member, such that the washer abuts the
closed end of the bridge member. The washer is preferably made from
hardened steel and serves to prevent damage to the closed end surface of
the bridge member when the cap screws are tightened in the tensioner.
In use, the present apparatus tensions the stud to a desired preload by
applying torque to each of the cap screws. The bridge member preferably
sits atop the bolted joint and covers the locking means which have been
engaged with the stud (e.g. the nut has been threaded onto the stud) and
tightened against the surface of the bolted joint. The hardened washer
preferably sits between the bridge member and the tensioning means (e.g.
multi-jackbolt tensioner), which is also threaded onto the stud and rests
against the washer on top of the bridge member.
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When the stud is placed under load, it is found that it elastically extends or
stretches according to 1-Tooke's Law within its elastic limit (i.e. it
undergoes elastic deformation along its length). The desired preload in the
stud can be divided between the number of cap screws in the tensioner, as
the individual loads on the cap screws combine to form the total load on the
stud. By knowing the individual load required for each cap screw, a torque
setting may be derived from established tables of load values, whereupon a
simple hand tool (e.g. torque wrench) may be used to apply the required
torque to each of the cap screws.
To ensure reliable tensioning of the bolted joint, the cap screws are
preferably tightened in a careful sequence which avoids any non-symmetric
loading of the cap screws. Therefore, a 'star' sequence for tightening the
cap screws is preferably adopted, in that the caps screws are tightened in an
order that preferably resembles the points on a star image, for example,
diametrically opposite cap screws are tightened one after another so that
symmetric loading of the jointed is achieved.
After initial loading, it is found that since the stud has extended, the nut
no
longer abuts against the surface of the bolted joint. Indeed, in practice an
air gap actually forms between the nut and the surface of the bolted joint,
as a result of the tension in the stud. The actuator may then be re-inserted
into the nut to preferably further tighten the nut to eliminate the air gap
and
enable the nut to bed down against the surface of the bolted joint.
Additional tightening of the cap screws may then be performed, with the
above procedure being repeated as often as necessary until the desired
preload is achieved in the stud.
Once the preload is attained, the cap screws may then be relaxed as the
tension in the stud (due to the action of the locking means) maintains
compression or loading of the bolted joint. The tensioner, bridge member
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and actuator may then all be removed from the bolted joint, leaving the
locking means in place to keep the joint together.
As a result, the removable components may then be advantageously re-used
to tighten a further bolted joint, without the need for another tensioner. The
only component that is not re-used is the locking means, but this is not as
elaborate (or as expensive) to replace as another tensioner. Of course, the
locking means may be subsequently re-used if it no longer becomes
necessary to maintain the bolted joint under compression.
The use of the locking means not only saves costs but also permits easy
maintenance of the bolted joint, as if it becomes necessary to release the
compression of the joint only one component need be relaxed (i.e. un-
tightened), as opposed to the multiple cap screws of conventional
tensioners -- which are themselves very quick to release. Hence, the present
invention provides significant advantages over the prior art and can
minimise downtime for maintenance arid repair etc.
According to a second aspect of the present invention there is a provided a
tensioning kit for use with a tensioner of a type such as a multi-jackbolt
tensioner, the kit comprising:
a locking means for engaging a stud in a bolted joint;
a bridge member arranged to at least partially enclose the locking
means and to receive the stud therethrough, the bridge member being
operable to transfer tension to the stud under the action of the tensioner;
and
an actuator operable to actuate the locking rneans through the bridge
member and to lock the locking means when a desired preload in the stud is
achieved.
The kit is most preferably used with a conventional nut-style multi-jackbolt
tensioner of the sort having a plurality of individual jackbolts or cap
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screws. However, as will be appreciated any suitable tensioner may be used
with the kit of the present invention.
It is to be appreciated that none of the aspects or embodiments described in
relation to the present invention are mutually exclusive, and therefore the
features and functionality of one aspect and/or embodiment may be used
interchangeably or additionally with the features and functionality of any
other embodiment without limitation.
F,mbodirnents of the present invention will now be described in detail by
way of example and with reference to the accompanying drawings in
which:
Figure 1 shows a side
cross-sectional view of a tensioning
apparatus according to a particularly preferred embodiment of the
present invention;
Figure 2 ¨ shows a plan view of an example tensioner as used in the
embodiment of Figure 1;
Figure 3 ¨ shows a top cross-sectional view of part of the apparatus
of Figure 1;
Figure 4 ¨ shows a side cross-sectional view of the non-removable
parts of the tensioning apparatus of Figure 1 after the stud has been
tensioned to the desired preload;
Referring to Figure 1, there is a shown a particularly preferred embodiment
of a tensioning apparatus 10 according to the present invention. It is to be
understood that the apparatus as shown in Figure 1 is not drawn to scale
and therefore the figure is intended for illustrative purposes only, but this
could represent any example bolted joint.
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The tensioning apparatus 10 comprises a locking means 12 adapted for
engagement with a stud 14, a removable bridge member 16 arranged to
enclose or cover the locking means 14 and a removable actuator 18
operable to actuate the locking means 14 through the bridge member 16.
5
In addition, the tensioning apparatus 10 also comprises a removable
tensioning means 20, which in this example is a nut-type rnulti-jackbolt
tensioner having a pitch circle diameter of cap screws 22 (although only
two cap screws are shown in cross-section in Figure 1).
As shown in Figure 1, the tensioning apparatus 10 is deployed in use
against an example bolted joint 24 having respective abutting flanges 24a
and 24b. The stud 14 passes through the flanges 24a, 24b and terminates in
a conventional nut 26. The bolted joint 24 could be any mechanical joint,
coupling or mechanical assembly that is intended to be compressed to a
desired load or tension.
It is to be appreciated, however, that although Figure 1 shows a stud 14 and
nut 26, this could alternatively be any form of mechanical fastener, such as
a bolt, headed fastener or cap screw etc.
In the example shown, the locking means 12 is a threaded nut, which
reciprocally engages the threading of the stud 14. In this way, the nut 12
may be simply screwed onto the stud 14 until it engages the surface of
flange 24a.
The nut 12 has a circular cross-section and comprises a plurality of radial
bore holes 12a through the body of the nut (as best shown in Figure 3). Any
number of bore holes may be used, but in the example discussed herein the
nut 12 has eight bore holes 12a.
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Each bore hole 12 defines a circular channel through the body of the nut
12, such that the channel has an axis that is approximately orthogonal to the
longitudinal axis of the nut. Each bore hole 12a extends fully through the
body of the nut (as shown in Figures 1 & 3), but could alternatively extend
only partially through the body (i.e. closed at one end ¨ the end closest to
the interior surface of the nut).
The function of the bore holes 12a is to receive the removable actuator 18,
in that the actuator 18 may be rcleasably engaged with a bore hole 12a (as
shown in Figures 1 & 3) to enable the nut 12 to be turned (i.e. screwed) on
the stud 14 so that the nut can be tightened. In this way, the nut 12 may be
locked (i.e. fully tightened) when a desired preload is achieved in the stud
14, as will be discussed in more detail below.
The removable bridge member 16 is cylindrical (e.g. tubular) in form and
comprises an open end 16a and a closed end 16b. The circumferential 'lip'
of the open end 16a acts as a 'surface' for engaging the surface of the
flange 24a; while the closed end 16b includes an open bore (e.g. circular
aperture) for receiving the stud 14 (as shown in Figure 1). In other words,
the bridge member 16 is placed over the stud 14 so that the stud passes
through and along the longitudinal axis of the bridge member.
Referring to Figure 1, when the bridge member 16 is placed over the stud
14, it covers the nut 12. .1Iowever, the bridge meniber 16 comprises an
aperture or window 17 through which the actuator 18 can pass to releasably
engage with the nut 12. The aperture 17 is located in the side wall of the
bridge member 16 and takes the form of a cut-out portion of the bridge
member.
in the example shown, the actuator 18 is in the form of an elongate rod,
such as a "tommy bar", fabricated from hardened steel. The tommy bar 18
may therefore be inserted through the aperture 17 of the bridge member 16
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to engage with a bore hole 12a (as shown in Figures 1 and 3), enabling the
nut 12 to be turned. The tommy bar 18 may then be removed and (re-
)inserted into the next bore hole 12a which has been rotated into the
aperture 17. In this way, the nut 12 may be turned and tighten.ed by
repeated application of the tommy bar 18 to the nut.
Referring again to Figure 1, the tensioning apparatus 10 further comprises a
washer 13 removably disposed between the multi-jackbolt tensioner 20 and
the bridge member 16, such that the washer 13 abuts the closed end 16b of
the bridge member. The washer 13 is made from hardened steel and serves
to prevent damage to the closed end surface of the bridge member 16 when
the cap screws 22 are tightened in the tensioner 20.
The use of a rnulti-jackbolt tensioner 20 is beneficial as it allows the many
advantages of this type of tensioncr to be utilised in the present
application.
Therefore, the stud 14 may be tensioned to relatively large preload tensions
by the application of only a relatively low torque to each of the cap screws
22. As a result, only simple hand tools or pneumatic devices need be used
to load the bolted joint to the required tension. This improves safety for the
installers, while also benefitting the environment as no heavy machinery
(e.g. bulky and/or high pressure hydraulic or electrical compressors) are
required saving power and expense.
Moreover, as multi-jackbolt tensioners tighten the stud in pure tension
there is no torsional strain, which eliminates the possibility of -thread
galling, as commonly occurs with direct torquing methods.
An example operation of the tensioning apparatus 10 will now be discussed
with reference to Figures 1 to 3. In use, the apparatus 10 tensions the stud
14 to a desired preload by applying torque to each of the cap screws 22.
The bridge member 16 sits atop flange 24a of the bolted joint and covers
the nut 12, which is threaded onto the stud 14 and tightened against the
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surface of the flange 24a. The hardened washer 13 sits between the bridge
member 16 and the multi-jackbolt tensioner 20, which is also threaded onto
the stud 14 and rests against the washer 13 on top of the bridge member 16.
When the stud 14 is placed under load, it is found that it elastically extends
or stretches according to Hooke's Law within its elastic limit (i.e. it
undergoes elastic deformation along its length). The desired preload in the
stud 14 can be divided between the number of cap screws 22 in the
tensioner 20, as the individual loads on the cap screws 22 combine to form
the total load on the stud 14. By knowing the individual load required for
each cap screw 22, a torque setting may be derived from established tables
of load values, whereupon a simple hand tool (e.g. torque wrench) may be
used to apply the required torque to each of the cap screws 22.
In the example of Figure 2, the cap screws 22 are simple hex nuts, which
may be tightened with an Allen key or similar tool.
To ensure reliable tensioning of the bolted joint, the cap screws 22 are
tightened in a careful sequence which avoids any non-symmetric loading of
the cap screws. Therefore, a 'star' or 'swan' sequence for tightening the
cap screws is preferably adopted, in that the caps screws are tightened in an
order that preferably resembles the points on a star image, for example,
diametrically opposite cap screws are tightened one after another so that
symmetric loading of the jointed is achieved (cf. Figure 2).
After initial loading, it is found that since the stud 14 has extended, the
nut
12 no longer abuts against the surface of -the flange 24a. Indeed, in practice
an air gap actually forms between the nut 12 and the flange 24a, as a result
of the tension in the stud 14. The tommy bar 18 may then be re-inserted
into the nut 12 to further tighten the nut to eliminate the air gap and enable
the nut to bed down against the surface of the flange 24a. Additional
tightening of the cap screws 22 may then be performed, with the above
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procedure being repeated as often as necessary until the desired preload is
achieved in the stud 14.
Once the preload is attained, the cap screws 22 may- then be relaxed as the
tension in the stud 14 (due to its inherent elastic restoring force) maintains
compression or loading of the bolted joint ¨ as it essentially pulls the nut
12 towards nut 26. As shown in Figure 4, the tensioner 20, bridge member
16 and tommy bar 18 rnay then all be removed from the bolted joint,
leaving the nut 12 in place to keep the flanges 24a and 24b together.
All components of the present apparatus and kit are manufactured from
high strength steel for safety and longevity of use, and each component
may be covered with a protective coating to enhance corrosion and rust
resistance. It should also be understood that no special training is required
to use the present apparatus and therefore even semi-skilled operators or
those with little engineering experience would be able to implement the
=
present invention.
Moreover, the present apparatus may be used in conjunction with load
indicating devices, particularly the load indicating washer disclosed in co-
pending application no. PCT/GB201.21052114 and as manufactured by
Clarki,vood Engineering Ltd., UK.
As will be appreciated from the foregoing embodiments, the present
invention is able to provide a simple, easy to fit/retro-fit, and cost-
effective
solution to reliably tension a mechanical joint to a desired preload.
Therefore, although the tensioning apparatus and kit are ideally suited for
ensuring an accurate and consistent tensioning of studs, bolts, threaded rods
and shafts etc., it will be recognised that one or more of the principles of
the invention may extend to other tensioning applications due, not least, to
the inherent scalability of the apparatus and kit.
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The above embodiments are described by way of example only. Many
variations arc possible without departing from the invention.
